package com.justnow.solution;

import jdk.nashorn.internal.ir.CallNode;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Solution1 {
    Map<String, String> phone = new HashMap<String, String>() {
        {
            put("2", "abc");
            put("3", "def");
            put("4", "ghi");
            put("5", "jkl");
            put("6", "mno");
            put("7", "pqrs");
            put("8", "tuv");
            put("9", "wxyz");
        }
    };

    List<String> output = new ArrayList<>();

    public void backtrack(String combination, String next_digits) {
        if (next_digits.length() == 0) {
            output.add(combination);
        } else {
            String digit = next_digits.substring(0, 1);
            String letters = phone.get(digit);
            for (int i = 0; i < letters.length(); i++) {
                String letter = phone.get(digit).substring(i, i + 1);
                backtrack(combination + letter, next_digits.substring(1));
            }
        }
    }

    public List<String> letterCombinations(String digits) {
        if (digits.length() != 0)
            backtrack("", digits);
        return output;
    }

    public static void main(String[] args) {
        Solution1 solution1 = new Solution1();
        String test = "234";
        List<String> strings = solution1.letterCombinations(test);
        for (String string : strings) {
            System.out.println(string);
        }
    }

}
